Anyone can lobby any public official in the United States. Any citizen or permanent resident has the right to lobby his or her elected officials about issues of concern on their own behalf. If a person is lobbying on behalf of a third part and is being paid to do so, he or she will likely have to register with the state or federal government. There is no limit on how many letters or e-mails can be written, phone calls can be placed, or visits can be made by an individual.
Groups of unaffiliated people (friends, family, survivors of cancer, bicycle safety advocates, etc.) may work together to lobby. However, any group that is registered as a 501(c)(3) nonprofit organization is limited in the amount of lobbying it can do as an official organization. Lobbying to some degree is allowed even for 501(c)(3) nonprofit organizations. The IRS measures the amount of lobbying and how much is OK with two tests: the “substantial part test” and the “expenditure test.” More information about these test and the IRS’ guidelines can be found at irs.gov.